Copending U.S. Pat. application Ser. No. 13,244 discloses a sample collection device for drawing samples of blood and other fluids for clinical testing purposes. The device includes a deformable vial, a non-vented cap removably secured to the open end of the vial, and a closure member for initially sealing the collection tube and, following the collection of a sample, for closing the vial itself. The cap includes an integral collection tube extending therefrom, the tube terminating in a tip which, instead of being blunt with an end face extending at right angles to the axis of the tube, is beveled to define an oval end face sloping at an angle of approximately 45.degree. with respect to that axis. For further details, reference may be had to such application and patent issuing therefrom, the disclosure of which is incorporated by reference herein.
A main aspect of this invention lies in the discovery that beveling the face of a tube for collecting samples of blood and other biological fluids has the important effect of reducing resistance that might exist to the entry of such fluids into the bore of the tube. The beneficial effects are particularly noticeable with fine-bore collection tubes formed of polypropylene, polyethylene, polystyrene, and other polymeric materials commonly regarded as being hydrophobic in nature. Blood and other biological fluids that would strongly resist entering the bore of such a tube if the end face were disposed at right angles, and such end face were then brought into contact with a supported drop of such a fluid, are found to enter the bore quite readily if the end face is disposed at an angle of approximately 35.degree. to 60.degree. measured from a plane normal to the axis of the tube. The preferred range is 40.degree. to 55.degree., with the optimum being approximately 49.degree. to 52.degree.. Beveling the tip as so described also yields important advantages even when the tube is formed of a material generally regarded as being hydrophilic, such as glass or cellulose acetate propionate. The ease with which biological fluids may be drawn into the bore of such a tube is noticably enhanced when the tip is beveled rather than blunt, and when the oval surface of the tip is brought into contact with a body of such fluid. Furthermore, when the tube is dimensioned to be filled by capillary action, the difference in tip construction is found to yield a decrease in the fill time for such a tube.
Capillary tubes for use in collecting samples of blood and other biological fluids without the need for producing a partial vacuum or suction effect at the opposite ends of such tubes, are commonly formed of hydrophilic materials, partly because the use of other materials would make it difficult or impossible to cause liquid to enter the tubes by capillary action, and partly because such other materials exhibit insufficient attraction to such liquids to overcome the internal forces of the liquids. An important aspect of this invention lies in the discovery that if the tip of a small bore capillary tube is beveled as described, resistance to entry of biological fluids into the bore of such a tube is sufficiently diminished that such tube may be used as a standard capillary tube, being filled by capillary or gravity action, notwithstanding the fact that such tube is formed of a hydrophobic polymeric material.
Other features, objects, and advantages of the invention will become apparent from the specification and drawings.